Electric fuse with trip device

ABSTRACT

A current limiting fuse structure characterized by a tubular, electrically insulating casing having spaced terminals thereon, one end of the casing being pivotally mounted on first terminal means and the other end of the casing being releasably mounted on second terminal means, a first fusible element within the casing and extending between the spaced terminals, trip means for unlatching the other end of the casing and comprising a plunger and a delayed explosive charge for driving the plunger against the second terminal means for releasing the other end of the casing from a second terminal means upon ignition of the delayed explosive charge, and a second fusible element extending between the terminal at said one end of the casing and the delayed explosive charge.

United States Patent 1 1 Blewitt I [111 3,825,871 [45'] July 23,1974

[ 1 ELECTRIC FUSE'WITH TRIP DEVICE [75] Inventor: Donald D. Blewitt, Pittsburgh, Pa.

[73] Assignee: Westinghouse Electric Corporation,

' Pittsburgh, Pa.

[22] Filed: Nov. 20, 1973 [21] Appl. No.: 417,693

[52] US. Cl. 337/171, 337/158 [51] Int, Cl. 1101b 71/20 [58] Field of Search ..337/17l,22l,203,21l, 337/172, 173, 174, 175, 176, 179, 158, 159, l 168, 169, 170

[56] References Cited UNITED STATES PATENTS 2,435,844 2/1948 Rawlins 337/171 3,134,874 5/1964 Cameron 337/158 3,265,838 8/1966 Ackermannw. 337/169 3,447,114 5/1969 Frink et al. 337/171 3,747,041

7/1973 Cameron 337/159 Primary Examiner-Harold Broome Attorney, Agent, or FirmL. P. Johns [57] ABSTRACT A current limiting fusestructure characterized by a tubular, electrically insulating casing having spaced terminals thereon, one end of the casing being pivotally mounted on first terminal means and the other end of the casing being releasablymounted on second terminal means, a first fusible element within the casing and extending between the spaced terminals, trip means for unlatching the other end of the casing and comprising a plunger and a delayed explosive charge for driving the plunger against the second terminal means for releasing the other end of the casing from a second terminal means upon ignition of the delayed explosive charge, and a second fusible element extending between the terminalat said one end of the casing and the delayed explosive charge.

9 Claims, 8 Drawing Figures t 1 LEC RIC FUSE WITH TRIP DEVICE I CROSS REFERENCE TO RELATED APPLICATION This invention is related to the invention disclosed in the application of Donald D. Blewitt, Ser. No. 344,015,

filed Mar. 22, 1973.

BACKGROUND OF INVENTION l. Field of the Invention: Thisinvention relates to current limiting fuses and more particularly to automatic latch opening means for n a dropout fuse assembly.

carrying elements of the fuse. When the fuse interrupts, r the retaining wire melts and the spring forces the plunger out. Trip devices serve two purposes including an indication that the fuse has blown and causing'an external action such as tripping a breaker or actuating a dropout mechanism that causes one end of the fuse to swing out of its holder.

n One disadvantage of the spring driven plunger type I is the relatively small amount of energy which can be stored in the spring. The strength of the spring is limited by the tensile strength, or gauge, of the restraining .difficult to design and manufacture a trip mechanism which-uses a wire of the requisite smallness, because the restraining wire must be smaller than the fusible element wire. Some European designs attempt to alleviate this problem by using. trip devices wherein the wire is doubled and tripled back on itself to increase the mechanical advantage and hence the strength of the wire,

but these are still relatively weak and are expensive and difficult to manufacture.

The weak force characteristic of the spring driven plunger imposes design restrictions on the device which it is to trip. Breaker trip mechanisms must be made overlysensitiveto assure reliable tripping by the fuse. Dropout type fuse mountings must be designed and built to critical tolerances and dimensions if they are to function correctly. Most dropout holders use an integral spring to effect the fuse ejection. This ejection spring is restrained by acomplex and expensive toggle mechanism whichis triggered by the fuse trip device. This spring force is in itself limited by the trip device force and by the necessity to force the fuse into the holder against the ejection spring. These constraints serve to compromise the performance of the assembly to the point where dropout cannot always be achieved against an external force such as ice build-up on the mounting.

Another shortcoming of the spring driven plunger trip device is that it cannot be used by itself to cause dropout of a full range current limiting fuse. The difficulty here lies in the area of low current clearing. If the wire. Since the wire is electrically in parallel with the instantaneous action of the trip device causes the fuse to dropout during low current clearing, the arc will follow the fuse down as it drops out with catastrophic results. This problem, and one method of delaying the plunger until current extinction, is more fully described in the above mentioned application Ser. No. 344,015.

SUMMARY OF THE INVENTION It has been found in accordance with this invention that the foregoing problem may be overcome by providing a'fuse structure comprising a generally tubular,

electrically insulating casing having spaced terminals thereon, one end of the casing being pivotally mounted on first terminal means and the second end of the casing being releasably mounted on second terminal means, a first fusible element extending between the spaced terminals, latch means for unlatching the sec:

ond end of the casing and comprising a plunger and a delayed explosive charge for driving the plunger against the second terminal means for releasing the second end of the casing from the second terminal means upon ignition of the delayed explosive charge, and a second fusible element extending between the terminal at said one end of the casing and the delayed explosive charge. 7

The advantage of the fuse structure of this invention is that it provides for a positive and reliable means for dropout mounting of a current limiting fuse.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a dropout fuse assembly partly in section;

FIG. 2 is a horizontal sectional view taken on the line II-II of FIG. 1;

FIG. 3 is a plunger type trip device of the type usable in the fuse of this invention;

FIG. 4 is a schematic view of another embodiment of this invention prior to release of the fuse;

FIG. 5 is a-view of the embodiment of FIG. 4 showing the fuse in the released position;

FIG. 6 is a plan view of a third embodiment of the invention; t FIG. 7 is a schematic view of the third embodiment prior toejection of the fuse; and

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 of the drawings a high voltage dropout, power fuse structure or assembly is generally indicated at 10 and it comprises standoff insulators l2 and 14 which support electrically conducting terminals 16 and 18. The terminals 16 and 18 in turn support the upper and lower ends, respectively, of a fuse 20. When the fuse 20 is in the latched or conducting position, electrical current may flow between the terminals 16 and 18 through the fuse. However, when an overload current is present fuseelements 22 may blow. It is desirable after the fuse elements have blown to disengage the fuse 20 from one of the terminals to serve as a visual indication that the fuse has operated and so that a possible path of electrical conductance which may result along the main body of the fuse 20 cannot conduct electrical current and thereby defeat the purpose of the fuse to provide an open circuit. In the particular dropelectrically conducting end ferrule 28 away from the combination latching mechanism and terminal 16. An end ferrule 30 remains in contact with the terminal 18. Consequently, an electrically insulating gap between the terminals 16 and 18 is created to prevent electrical conduction under even relatively high voltage stress.

As shown in FIG. 1 the fuse 20 comprises a generally tubular electrically insulating casing 32, the end ferrules 28 and 30, the fusible elements 22, a fusible elementor wire 34, and a propellant driven trip device 36. As shown in FIG. 1 the fusible elements 22 extend longitudinally of the fuse 20 with their lower and upper ends secured to their corresponding ferrules 28 and 30 in an electrically conducting manner. The lower end of the fusible wire 34 is likewise connected to the lower ferrule 30, but the upper end is attached to the trip device in a manner disclosed in FIG. 3.

The trip device 36, which is more particularly shown in FIG. 3, comprises a tubular member 38 providing a chamber 40 in which a plunger 42, having an enlarged head 44, is disposed for longitudinally movement. The lower end of the chamber 40 contains a propellant charge 46 of an explosive material or of a gas producing material. To provide for a time delay the lower end of the chamber 40 communicates with a conduit 48 of reduced cross section which communicates with a second chamber 50. The chamber 50 is filled with the explosive 46 (which also occupies the conduit 48) and is sealed with an electrically insulating plug 52. The upper end of the fusible wire 34 extends through the plug 52 and into the explosive charge 46 in the chamber 50.

When the-fusible elements 22 blow or melt, the full supply voltage is momentarily connected between the fusible wire 34, which has a higher coefficient of resistance than that of the fusible elements 22, and the member 38. As a result, the propellant charge 46 in the chamber 50 is ignited or sparkover and the fusible element 34 is burned back. The time delay, which is adjustable by controlling the dimensions of the conduit 48, is timed so that all current has been shut down by .the fuse action before the plunger 42 is driven out of the chamber 40. Delays of four seconds or more are easily obtainable. Since'the fusible wire or ignition wire tically any value required. The gap flashover voltage may be varied to suit the various fuse designs. Asshown .in FIG. 1 when the plunger 42 is driven outwardly, it strikes an ejection member 54 having an upwardly and outwardly inclined surface and causes the upper end of the fuse 20 to move in the direction of the arrow 24 around the pivot 26.

Anotherembodiment of the invention is shown in FIGS. 4 and which differs from that described in FIGS. 1-3 in that an ejector or L-shaped member 56 (FIG. 4) is pivotally mounted at 58 on the insulator 12. When theplunger 42 is ejected upwardly against the horizontal portion of the ejector 56, a lower vertical portion 60 is propelled or rotated counterclockwise against the fuse to cause the fuse to kick out of the mounting clip 61 and to rotate clockwise in the direction of the arrow 62 as shown in FIG. 5.

Another embodiment of the invention is shown in FIGS. 6, 7, and 8 in which the fuse 20 is provided with a plunger 64 which is part of a trip device similar to the trip device 36 (FIG. 3), but disposed laterally with respect to the longitudinal axis of the fuse 20. The upper end portion of the fuse 20 is mounted between spaced portions of a mounting clip 66 where it is normally retained during operation of the fuse. When the fuse elements 22 in the fuse 20 melt, as described above with respect to FIG. 1, the plunger 64 (FIG. 7) is driven outwardly to the left (FIG. 8) against the assembly of the insulator 12 and clip 66, causing the fuse to move clockwise in the direction of the arrow 68 and out of the mounting clip 66.

In conclusion, the trip device of this invention may be applied to both current limiting and expulsion type fuses. Because of the built-in time delay, full range current limiting dropout fuses are feasible. Since the plunger force can be made quite large, it is possible to achieve a large simplification (and cost reduction) in the design of dropout fuse holders. Moreover, the plunger should have a sufficient force to break free of any practical ice buildup. As in current practice, the lower end of the fuse is equipped with a hinged device to allow the top portion to swing free when disengaged.

What is claimed is:

1. A fuse structure comprising a generally tubular, electrically insulating casing having spaced terminals thereon, one end of the casing being pivotally mounted on first terminal means and the other end of the casing being releasably mounted on second terminal means, a first fusible element extending between the spaced terminals, trip means for unlatching the other end of the casing and comprising a plunger and an expulsion charge for driving the plunger against the second terminal means for releasing the other end of the casing from the second terminal means upon ignition of the expulsion charge, and a second fusible wire extending between the terminal at said one end of the casing and the expulsion charge.

2. The fuse structure of claim 1 in which the second fusible wire has an electrical resistance greater than that of the first fusible element.

3. The fuse structure of claim 1 in which the trip means comprises an explosive containing chamber having a time-restrictive passage between opposite end portions thereof.

4. The fuse structure of claim 3 in which the second fusible wire extends into the explosive charge in the portion of the chamber remote from the plunger.

5. The fuse structure of claim 1 in which the second terminal means comprises a fuse ejecting member cooperative with the plunger for moving the casing away from the second terminal means.

6. The fuse structure of claim 5 in which the fuse ejecting member is an outwardly inclined surface against which the plunger is propelled.

7. The fuse structure of claim 5 in which the fuse ejecting member is a lever against which the plunger is propelled.

8. The fuse structure of claim 5 in which the plunger is disposed longitudinally of the axis of the fuse.

9. The fuse structure of claim 5 in which the plunger is disposed laterally of the axis of the fuse. 

1. A fuse structure comprising a generally tubular, electrically insulating casing having spaced terminals thereon, one end of the casing being pivotally mounted on first terminal means and the other end of the casing being releasably mounted on second terminal means, a first fusible element extending between the spaced terminals, trip means for unlatching the other end of the casing and comprising a plunger and an expulsion charge for driving the plunger against the second terminal means for releasing the other end of the casing from the second terminal means upon ignition of the expulsion charge, and a second fusible wire extending between the terminal at said one end of the casing and the expulsion charge.
 2. The fuse structure of claim 1 in which the second fusible wire has an electrical resistance greater than that of the first fusible element.
 3. The fuse structure of claim 1 in which the trip means comprises an explosive containing chamber having a time-restrictive passage between opposite end portions thereof.
 4. The fuse structure of claim 3 in which the second fusible wire extends into the explosive charge in the portion of the chamber remote from the plunger.
 5. The fuse structure of claim 1 in which the second terminal means comprises a fuse ejecting member cooperative with the plunger for moving the casing away from the second terminal means.
 6. The fuse structure of claim 5 in which the fuse ejecting member is an outwardly inclined surface against which the plunger is propelled.
 7. The fuse structure of claim 5 in which the fuse ejecting member is a lever against which the plunger is propelled.
 8. The fuse structure of claim 5 in which the plunger is disposed longitudinally of the axis of the fuse.
 9. The fuse structure of claim 5 in which the plunger is disposed laterally of the axis of the fuse. 